Whatever you thought of Margaret Thatcher — and during an unbroken stretch in office from 1979 to ’90, the former Prime Minister, who died on April 8 after a stroke at the age of 87, attracted both passionate support and deep loathing — you never doubted her force of will. The Iron Lady showed her mettle again and again, wrenching Britain, often brutally, out of a malaise and sense of all-encompassing failure that had blighted it for much of the era after the end of World War II. This meant not only facing down opponents but also critics in her own party, who ran scared as the strong economic medicine she prescribed sickened swaths of voters. “To those waiting with bated breath for that favorite media catchphrase, the U-turn, I have only one thing to say,” she declared at the 1980 Conservative Party conference. “You turn if you want to. The lady’s not for turning.”

Britain keeps state papers secret for 30 years. A trove released at the end of 2011 revealed a leader who might have been more sensitive to public opinion, and counterarguments, than legend suggests. In July 1981 she authorized secret contacts with Irish republicans to try to halt the hunger strike by Irish Republican Army (IRA) prisoners that would see 10 of their number starve themselves to death. During the same month she fended off hard-liners in her Cabinet who proposed consigning the riot-torn city of Liverpool to “managed decline.” But these stirrings — of conscience or pragmatism — also prove that she was prepared to override resistance from those closest to her. Indeed, her peremptory manner with her own colleagues attracted the attention of Britain’s inspired satirical TV puppetry show, Spitting Image. In one sketch Thatcher and her Cabinet are seated in a restaurant. She orders raw steak. “And what about the vegetables?” the waiter inquires. “Oh, they’ll have the same as me,” Thatcher replies.

A Boudicca, she led her nation into battle in the Falkland Islands and fought off attempts to draw the U.K. into a closer political embrace with Europe. “She has the eyes of Caligula and the mouth of Marilyn Monroe,” observed French President François Mitterrand, revealing the queasy mixture of antipathy and attraction she stirred in many of her male associates.

Ronald Reagan’s feelings for his helmet-haired, be-handbagged friend in Westminster were more clear-cut. She was his ideological soul mate and theirs was a truly special relationship. Together they reinvigorated political conservatism, and by refusing to believe that history moved in only one direction, led a challenge to Soviet communism that in the end saw its fall.

As the first female Premier not only of Britain but also of any leading industrial democracy, she forged a template by which women anywhere might measure their ambitions. At the time, many of us in the U.K. found it impossible to savor her achievements. Most brands of feminism held that women were (at least) as capable as men of governing, but there was also an anticipation that we would bring different qualities to the job, not least empathy for the underdog, a consensual approach and a determination to do right by the sisterhood. Thatcher appeared to glory in her utter lack of these instincts, stigmatizing the poor as work-shy, decrying consensus politics as “the process of abandoning all beliefs, principles, values and policies” and averring “I owe nothing to women’s lib.” In 2009, I mentioned to a friend, who had also lived through Thatcher’s polarizing reign, that I had just encountered our old bête noire at a party. More than a quarter of a century had elapsed since we had marched down a street chanting, “Maggie, Maggie, Maggie! Out, out, out!” but my friend reacted with undiminished hostility. “Why didn’t you punch the old bag?” she snarled.

In truth I had long since revised my views of “Maggie.” You can argue that her economic reforms ought to have been introduced with greater care for their social impact, but not about whether most of them were necessary. The history of Thatcherism is also a history of the failure of the left to articulate any viable alternative. This analysis was shared by Tony Blair, who was able to build on Thatcher’s economic legacy after remodeling the Labour Party into an electable force.

But even if I still harbored resentments, the frail woman I encountered at the U.S. ambassador to London’s Christmas drinks evoked quite different emotions. A year previously, her daughter had publicly confirmed that her mother was suffering from dementia; the initial symptoms appeared in 2000. I first saw the evidence of this deterioration at a photo shoot for TIME in 2006. A devoted assistant and a brace of security officers ushered a woman with disheveled hair and a crumpled face into the studio. As the hairdresser and makeup artist plied their skills, so the familiar, imposing figure emerged and with this transformation came renewed clarity and a graciousness that endeared her to the team working on the shoot. The only residual sign of her decline was her unshakeable conviction that Mikhail Gorbachev would shortly join us, no matter how many times I assured her he would not.

This was not simply the dementia talking. There had never been a plan to photograph the former leaders together, but TIME had photographed Gorbachev the day before, for an issue of the magazine featuring the Europeans who had done most to shape the world in the 20th century. Even before President Reagan, Thatcher spotted in Gorbachev, who became General Secretary of the Soviet Communist Party in 1985, “a man we can do business with.” She helped persuade a skeptical Washington that glasnost and perestroika were for real, and that some at least in Moscow had understood that their bankrupt society could not continue in the ways that it had done before. When the Berlin Wall fell in 1989, Europe’s annus mirabilis, she had her vindication.

Yet in a curious sense, the end of the Cold War was also her political undoing. She would not accept, as her contemporaries Mitterrand and German Chancellor Helmut Kohl did, that a new, post-Soviet architecture was needed in Europe. As the U.S. gratefully looked at Europe as “job done” and turned its attention to other matters in the world — the dysfunction and violence of the Middle East, the rise of China — she stood obdurate against the impulse toward closer political and economic integration of the European nations, helping to foster divisions in her own party that would eventually lead to her ouster and are once again widening the Channel between Britain and the rest of Europe. In November 1990, she lost the Conservative leadership and was driven from Downing Street with tears glistening in her eyes.

It was a rare defeat for someone who had beaten Britain’s class system and dusty attitudes to women in the workplace to rise to the summit of public life. Margaret Hilda Roberts was born in 1925, the daughter of a small-town storekeeper in Lincolnshire, a featureless county in the east of England. Devoted to her father — who served as an alderman and mayor in their town — she took a degree in chemistry at Oxford, where she first dabbled in Conservative Party politics. She married Denis Thatcher, a successful businessman, 10 years her senior, in 1951, and two years later gave birth to twins, Mark and Carol. After an arduous battle to convince her own party and voters that she had the right stuff to be a politician, she won a seat in Parliament for Finchley, a constituency in North London, in the 1959 election, and was quickly recognized for her intelligence and energy. From 1964 to ’70, the Labour Party governed Britain, but when the Tories, against the odds, won the 1970 election, Edward Heath, the new Prime Minister, made her Secretary of State for Education and Science. After Heath lost power in 1974, she ran against him as party leader in 1975 and, to the astonishment of Britain’s famous chattering classes, was successful. In 1979, as the minority Labour government of James Callaghan floundered and Britain’s antediluvian labor unions visited their grievances on long-suffering voters, her party won a decisive victory. She secured two more terms of office, in 1983 and ’87, extending her majority in the House of Commons on both occasions, at the time an unprecedented feat in modern British political history.

As Prime Minister, Thatcher was motivated by a few simple principles. Government regulation — and confiscatory taxation — neutered the animal spirits of capitalism; the world was a dangerous place, in which it paid to be on one’s guard; Britain was not finished; communism was an evil that threatened the world and stunted the life chances of those who had to live under its heel. But beyond that, she understood what it was that a significant strand of ordinary people wanted from political leaders: not necessarily ringing phrases and great speechifying (though she could certainly do that), but a sense that decent lives, decently lived, were worthwhile; that growing prosperity was not a sign of capitalism’s rapaciousness but the mechanism by which families could live a little better each year.

In the first few years of her first term in office, she squeezed inflation out of the British economy and made plain that those enterprises that could not compete in the modern world would not be rescued, as had been the case under her predecessors. Britain, the world’s first industrial nation, saw its smoke-blackened heartlands rendered into rust heaps. As unemployment climbed and riots broke out in the cities, her position appeared precarious. But by 1982, the economy was beginning to show the first signs of life. That spring, she refused to accept that the Argentine invasion of the Falkland Islands was a done deal and dispatched her armed forces across the Atlantic to fight a fierce little war. Triumphant, she won re-election in 1983 and then took on the coal miners — the vanguard of the old left-wing English working class — crushing them in a yearlong strike. Like many of her victories, the casualty toll was high, with communities blighted and families plunged into grinding poverty with no means of escape.

She had arrived in Downing Street in 1979 improbably quoting St. Francis of Assisi. “Where there is discord,” she intoned, “may we bring harmony; where there is error, may we bring truth; where there is doubt, may we bring faith; and where there is despair, may we bring hope.” She failed in the first objective at least, and the human costs of Thatcherism — and the unequal distribution of hope — mean she may prove almost as divisive in death as in life, as Britons squabble over her legacy. At her own request she will not be granted a state funeral, though many believe she deserves one.

There are those, like my friend, who feel a more appropriate response would be to dance on her grave. I cannot share that view, and not only because I believe Thatcher left Britain, on balance, in better shape than she found it. Politicians have forfeited public trust in recent years, relying too heavily on spin and connecting too little with voters. Thatcher’s greatest flaws — a strength of conviction that brooked few moderating influences, a strength of character that rendered her viscerally incapable of understanding human vulnerabilities — were also her greatest assets. There was little difference between the public figure and private one. She was motivated by her belief in what she could deliver to public office, not by what public office could deliver to her.

So when she clutched my arm at that Christmas drinks party, I wasn’t tempted to recoil. She seemed disoriented and a little anxious. Now even the teased hair and mask of makeup couldn’t disguise that she had become the sort of person she once least understood: someone incapable of looking after herself. A colleague attempted to engage her in conversation about world affairs, but she stared at him, blankly. I commented instead on her clothing. In recent years she had taken to wearing shades of deep rose and magenta instead of her signature blue. “I do think pink is such a friendly color,” she said.

The 2011 biopic The Iron Lady focused on the poignancy of Thatcher’s declining years. While Meryl Streep’s performance in the title role was uncannily accurate, the film’s depiction of Thatcher’s legacy was far less so. That she overcame obstacles of class and sex to rise to power tempered her resolve, but it isn’t the reason she will be remembered as one of the most significant leaders of the 20th century.

By standing shoulder to shoulder with Reagan and calling Soviet communism for what it was — a cruel sham, an economic failure — she helped liberate those Russians and East Europeans who had spent generations with their dreams on hold. Many of her own countrymen will never accept that she performed a similar function for Britons. She was not an empathetic person, not one to suffer fools gladly (or at all), not one who could appreciate that men, women and families could imagine different ways to a satisfying life from the one that she thought best. She was hardheaded, perhaps hard-hearted. She was that most polarizing of beings: a conviction politician. In our current age of weak leaders transfixed by oncoming global crises like rabbits in the headlights, it’s sobering to realize that the Lady’s not for returning.